Literature Review

The relationship between siblings is the longest, most complex, and most important bond one can have in life; but it becomes further complicated when one of the siblings is developmentally disabled (DD), intellectually disabled (ID), and/or physically disabled (O’ Neill & Murray, 2016; Tomeny et. al., 2017b; Moss et. al., 2019). Adult typically-developed siblings (TD sibs) of individuals with disabilities are often overlooked by health professionals, academic scholars, and society. However, one's lifetime experiences as a sibling to an individual with disabilities is crucial to understanding their mental health in adulthood. Currently, there are a variety of research studies that have produced contradictory results regarding the mental well-being and the sibling relationship of adult siblings of individuals with disabilities. This literature review will focus on analyzing the results of studies pertaining to the quality of sibling relationships between disabled and TD siblings; research regarding the mental health of adult TD sibs; and studies that find correlations between these two topics.

Quality of Sibling Relationships

Tozer and Atkin conducted a qualitative study (2014) to analyze the expectations for adult siblings to provide long-term social support for their adult brother or sister with autism spectrum disorder (ASD). They found that “nearly all siblings described growing up with a ‘chaotic’ family life and one often constrained by the need to adapt ‘autism-friendly’ routines” (Tozer & Atkin, 2014, p. 345). Despite having a childhood that centered around their sibling with ASD, about ⅔ of participants reported that they currently have a strong sibling relationship due to being actively involved in their sibling’s life (Tozer & Atkin, 2014). However, a “strong” sibling relationship doesn’t necessarily suggest that it’s composed of positive experiences and emotions; rather, it implies that the TD sibling has a strong sense of commitment and obligation to their sibling with ASD. Tozer and Atkin discovered that most TD adult siblings - even those with a strong sibling connection - “expressed sadness and frustration” regarding their limited relationship, such as “a sense of loss at not having a typical, mutual sibling relationship” (2014, p. 346). Tozer and Atkin’s research on the relationship between TD adults and their siblings with ASD show that the sibling relationship is very complex and is a different experience for each family (2014). Rossetti and Hall used a similar qualitative approach and found that even strong or close sibling relationships between adult TD sibs and their sibling with severe disabilities are full of many difficulties (2015).

Rossetti and Hall recruited participants through SibNet, the Facebook group that I sent my survey to, and are both siblings of brothers with ID. Their study found that about 57% of participants described their current relationship with their sibling as close (Rossetti & Hall, 2015). Rossetti and Hall coded responses about experiences that influenced the relationship under the theme “characteristics of the brother/sister” with disabilities (specifically their diagnosis, social difficulties, communication needs, and behavioral challenges) (2015). Responses regarding perceptions of the relationship were coded as themes of closeness and the emotional impact of the relationship (Rossetti & Hall, 2015). Rossetti and Hall (2015) found that adult TD sibs with a sibling with ASD were more likely to describe their sibling relationship as not close, which supports findings from Hodapp and Urbano (2007) as well as Orsmond, Kuo, and Seltzer (2009). Additionally, this study had a novel and significant discovery in that limited communication skills by an individual with severe disabilities impacts the closeness of the sibling relationship (Rossetti and Hall, 2015). In response to questions pertaining to the emotional impact of having a sibling with severe disabilities, many adult TD sibs reported feelings of guilt, frustration, joy, and stress related to their sibling relationship, as well as current and future caregiving responsibilities (Rossetti & Hall, 2015).

Mental Well-being of Adult Siblings

Some research focuses on the diagnosis of a mental illness disorder (depression, anxiety, OCD, PTSD, etc.) in adult TD siblings. Howlin, Moss, Savage, Bolton, and Rutter (2015) had a unique longitudinal study that categorized adult sibs of individuals with ASD as either being unaffected by autism (UA) or as having a Broader Autistic Phenotype (BAP). BAP is defined as the criteria used to identify individuals who present with autistic traits but are below the clinical cutoff for a diagnosis of ASD (Howlin et. al., 2015). While assessing mental health outcomes of adult sibs was one of the study’s main goals, the mental health questionnaire results were generally inconclusive. However, Howlin et. al. were able to conclude that UA adult TD sibs were less-likely to have OCD-related problems than adult sibs with BAP (2015). The researchers suggest that the high frequency of OCD occurrence in adult sibs with BAP is related to the characteristic obsessive-like behaviors of individuals diagnosed with autism; thus, the presence of obsessive behaviors may have been a contributing factor in the initial BAP diagnosis (Howlin et. al., 2015). This is a significant study because multiple research studies prior to it had produced contradictory conclusions regarding the mental well being of siblings of individuals with ASD. Some of these studies had found a heightened risk for developmental, emotional, and/or behavioral problems while others concluded there was no evidence of increased difficulties among sibs and “yet others reported above average levels of psychosocial and emotional adjustment” (Howlin et. al., 2015, pp. 707). Howlin et. al. infer that the inconsistent findings of these previous studies occurred because the researchers grouped UA sibs and sibs with BAP together when they should have been studied independently from each other. When unaffected adult TD sibs are studied separately, results have found that they are generally high-functioning individuals who have better life and mental health outcomes (Howlin et. al., 2015). Drawing from this conclusion, a linked study was conducted that assessed function (via IQ levels) and the mental health outcomes of UA adult TD siblings of individuals with ASD (Moss, Eirinki, Savage, & Howlin, 2019).

Moss et. al.’s study in 2019 found that all of the TD sibling participants had at least an average IQ; however, about half of the participants “had scores at or above the suggested level for clinical caseness” of psychiatric disorders such as OCD, bipolar, depression, anxiety, and PTSD (p. 46). These results led to the significant conclusion that TD siblings had more difficulties regarding their mental health than the general population; however, Moss et. al. found “little or no direct association between functioning in adulthood and the experiences of having a sibling with autism” (2019, p. 49). Yet, the majority of TD participants had serious anxieties about the future of their sibling(s) with ASD, which could contribute to an individual’s psychiatric disorder (specifically anxiety and/or depression) (Moss et. al., 2019). Research with a similar, but more specific, focus was conducted by O’Neill and Murray in 2016 when they compared adult TD sibs’ anxiety and depression symptoms with the general population. Contrary to Moss et. al. (2019), who studied siblings of individuals with ASD, O’Neill and Murray (2016) sampled from a broader population - adult siblings of individuals with DD (autism is a type of developmental disability).

O’Neill and Murray discovered that adult TD siblings of individuals with ASD or Prader-Willi syndrome (PWS) were significantly at-risk for anxiety, while adult TD siblings of individuals with ASD or DD were more vulnerable for depression (2016). Additionally, they found that TD adult sibs who are younger than their sibling with disabilities are more likely to have depression and/or anxiety symptoms than adult TD sibs who are older, regardless of their sibling’s diagnosis (O’Neill & Murray, 2016). O’Neill and Murray suggest that positive relationships between TD and DD adult siblings would theoretically increase positive emotions for both siblings, which would potentially reduce anxiety and/or depression symptoms in adult TD sibs (2016). However, further research regarding adult TD anxiety/depression vulnerabilities and the quality of sibling relationships needs to be done. As shown in the section below, some studies implicitly evaluate the mental well-being of TD siblings by focusing on the quality of sibling relationships.

Correlational Studies: Adult Siblings’ Mental Health and Sibling Relationships

Orsmond, Kuo, and Seltzer investigated the sibling relationship and overall well being among adolescent and adult TD sibs of individuals with ASD (2009). Other studies by O’Neill and Murray (2016) and Moss et. al. (2019) reported that TD siblings of individuals with disabilities (specifically those with ASD or DD) displayed higher levels of depressive symptoms. Contrary to these findings, Orsmond et. al. reported the average scores for both adult and adolescent TD siblings of individuals with ASD on a depression questionnaire were “considerably lower” than the cutoff point for clinical depression (2009, p. 75). The only conclusion Orsmond et. al. provided that could explain this deviance was that adolescents used different coping styles than adult TD sibs did; however, this is expected due to age differences (2009). Additionally, Orsmond et. al. found that the quality of sibling relationships are impacted by family characteristics (size of family, gender of the siblings, and age of the sibling with ASD), regardless if the TD sibling is an adolescent or an adult (2009). This study had a significant conclusion that behavior problems in the sibling with ASD “negatively impacted the sibling relationship. Behavior problems may make siblings less willing to engage in activities with their brother or sister with an ASD, especially activities in public contexts” (Orsmond et. al., 2009, p. 76). Even though Orsmond et. al. (2009) focused on adolescent and adult TD sibs of individuals with ASD, this significant conclusion is similar to one observed by Hodapp and Urbano (2007). Hodapp and Urbano found that sibling relationships were negatively impacted when the sibling with disabilities (regardless of ASD or Down syndrome diagnosis) had higher levels of emotional and/or behavioral problems (2007).

Hodapp and Urbano (2007) assessed how sibling relationships among adult siblings of adults with Down syndrome compared to those of adult TD sibs of adults with ASD. Previous research has found a “Down syndrome advantage,” which is a general conclusion that “families of persons with Down syndrome generally cope better (compared [to] families of children and adults with other disability conditions)” (Hodapp & Urbano, 2007, pp. 1019). Hodapp and Urbano also found a Down syndrome advantage among TD adult sibs, specifically regarding sibling relationships; “overall, the relationships between siblings and their brothers/sisters with Down syndrome were closer and more positive than were relationships of siblings with their brothers/sisters with autism” (2007, p. 1023). The researchers found that adult TD siblings of all ages showed a Down syndrome advantage regarding better sibling relationships, better health outcomes with lower levels of depressive symptoms, and an increase in the amount of time spent with sibling (Hodapp & Urbano, 2007). Hodapp and Urbano’s (2007) findings about the Down syndrome advantage in adult TD sibs is supported by a significant conclusion established in a study conducted by Tomeny, Barry, Fair and Riley (2017a).

Tomeny et. al. found that adult TD sibs who reported positive attitudes about their sibling relationship were more likely to give their sibling an increased level of aid (2017a). Additionally, the same group of TD sibs reported lower levels of depression and stress symptoms, which indicates an increase in life satisfaction (Tomeny et. al., 2017a). Tomeny et. al. discovered that “TD siblings of those with ASD may be at greater risk for depression and stress and for providing less aid/support due to lower levels of positive sibling relationship attitudes” (2017a, p. 112). Thus, having a positive attitude about the sibling relationship leads to better life outcomes for both siblings. Based on the results in their 2017a study, Tomeny et. al. decided to conduct a parallel study which found that a positive sibling relationship, often established in childhood through sibling-focused parentification, indicates that adult TD siblings who are engaged in activities with their sibling diagnosed with ASD and are more likely to think positively about them (2017b). However, sibling-focused parentification could cause lasting effects on adult TD siblings’ mental health.

Tomeny, Ellis, Rankin, and Barry’s 2017b study focused on how different types of childhood parentification are related to adult TD sibs’ mental health outcomes and attitudes towards their sibling relationship. There are two types of parentification: parent-focused occurs when children take on caregiver roles and responsibilities to care for their parents. Sibling-focused parentification occurs when siblings take on caregiver roles and responsibilities to care for their siblings; for this study, sibling-focused parentification is identified when the TD sib cares for their sibling with ASD (Tomeny et. al., 2017b). Tomeny et. al. asked adult sibling participants to retrospectively self-report their childhood experiences related to taking care of their sibling with ASD in order to identify signs of sibling-focused parentification (2017b). Tomeny et. al. discovered that “sibling-focused parentification was a unique predictor of positive sibling relationship behavior and cognitions” (2017b, pp. 1063). However, participants who reported using sibling-focused parentification in childhood also reported higher levels of stress and anxiety throughout their lifetime (Tomeny et. al., 2017b).